Drilling method and bit

ABSTRACT

A diamond-type bit of certain cross-sectional configuration and a method for drilling a slim hole wellbore wherein the bit is rotated at a high rate during drilling.

United States Patent Hoffman et al. [4 Oct. 17, 1972 [54] DRILLING METHOD AND BIT 2,264,617 12/1941 Carpenter etoll ..'...175/329 [72] Inventors: Robert N. Hoffman, Richardson; p 1 2,953,354 9/1960 Williams .,....,...175/329 [73] Assignee: Atlantic Richlield Company, New 3,027,952 4/1962 Brooks ..175l329 York. N.Y. R25,3I9 l/l963 Short 175/329 [22] Filed: Feb.2, 1971 3,599,736 8/1971 Thompson ..l75/J29 [21] Appl. No.: 111,831 Primary Examiner-David H. Brown Attorney-Blucher S. Tharp and Roderick W. Mac- Donald [52] US, Cl. ..l75/329 [51] Int. Cl. ..E21b 9/36. [58] Field of Search "175/327, 329, 330,421, 7, ABSTRACT 175/409-4111? A diamond-type bit of certain cross-sectional configu 1 ration and a method for drilling a slim hole wellbo're [56] References Cited UNITED STATES PATENTS Gstalder et al. 175/329 wherein the bit is rotated at a high rate during drilling.

7 Claims, 3 Drawing Figures mm mm 3.698.491

SHEET 1 0F 2 FIG. I

INVENTORS I ROBERT N. HOFFMAN FIG. 2 1.0m R. KERN ATTORNEY PATENTEDHBTITIQYZ 3.698.491

SHEET 2 OF 2 INVENTORS ROBERT N. HOFFMAN LOYD R. KERN ATTORNEY DRILLING METHOD AND BIT BACKGROUND OF THE INVENTION ration and the round nose configuration discussed hereinafter in detail.

In employing bits of the above conventional longitudinal cross sectional configurations in slim hole drilling wherein small diameter wellbores, e.g. no larger than about 6 inches in diameter, are drilled using high rates of bit rotation, e.g. at least 500 rpm, excessive wear of the cutting elements in at least the shoulder portion led to unacceptably short drilling life for the bits.

SUMMARY OF THE INVENTION which class is not limited solely to the use of diamonds as cutting elements. This class encompasses the use of substantially any hard particle in addition to diamonds such as tungsten carbide or cubic boron nitride as a cutting element. Thus, the term diamond-type bit in this invention is not limited to a particular bit which has only diamonds as its cutting elements, but rather encompasses all bits of the class of diamond-type bits which have particles of any hard material as cutting elements. 7

This invention also relates to a method for drilling a slim hole wellbore using high rotational rates for the drill bit and also using bits having the particular longitudinal cross-sectional configuration of the bits of this invention.

Accordingly, it is an object of this invention to provide a new and improved drilling bit. It is another object to provide a new and improved bit for use in high speed rotational procedures such as slim hole drilling. It is another object to provide a new and improved method for slim hole drilling. It is another object to provide a new and improved bit for slim hole drilling procedures.

disclosure and the appended claims.

DETAILED DESCRIPTION OF THE INVENTION FIG. 1 shows a double-cone cross-sectional configuration for a bit as known in the prior art.

FIG. 2 shows the specially modified parabolic crosssectional configuration of a bit according to this invention.

FIG. 3 shows a plan view of a bladed diamond-type bit according to this invention.

' More specifically, FIG. 1 shows a portion of a bit parallel to the longitudinal axis 1 of-the bit, the portion being composed of a shoulder section 2 which extends from the point of full gauge 3 to the nose 4. The point of full gauge on a bitis the point at which the bit reaches its full diameter so that 180 opposed points of full gauge determine the diameterof the borehole to be drilled. A line between these opposed points is the full gauge diameter. 'One half of thefull gauge diameter, e.g., starting at the longitudinal axis 1 and extending to the point of full gauge 3, is the full gauge radius. The nose of the bit is the point or area of the bit which first touches the rock to be drilled and can be an area of finite width as shown for nose area 4 or can be simply a line of substantially no width which circumscribes the throat area 5 of the bit. The nose is the transition line or area between the shoulder region 2 and the throat regionS. V I g v The longitudinal cross-section shown in- FIG. 1 is known in the art as a double-cone cross-section in that portion 6 of shoulder 2 is part of a substantially straight conical surface which extends around the bit in the shoulder region, this conical section 6 being at an angle-E with respect to a full gauge diameter line which intersects longitudinal center line 1 at a 90 angle. The central portion of throat region 5 also contains a conical section 7 which is at an angle F with respect to a full gauge diameter line as described above with respect to angle-E. The transition area 8 between conical section 6 and nose 4 and the transition area 9 between conical section 7 and nose 4 are composed of curved surfaces described by radii of curvature 8' and 9'. The pivot points 10' and 11' for 8' and 9', respectively, are on dotted lines 10 and 11 which extend from the outer and inner, respectively, sides of nose area 4 and which also extend substantially parallel to longitudinal center lin 1, the pivot points being at points 10' and 11 In the prior art round nose configuration, the

' shoulder region from the point of full gauge to the nose Other aspects, objects, and advantages of this invention will be apparent to those skilled in the art from this would be a section of a circle and there would be no conical section 6 or curved but non-circular section 8' in the round nose configuration. In the round nose configuration, the throat region can be as shown for the double-cone configuration of FIG. 1 or the conical section 7 can be eliminated and a curved section can extend from nose 4 to the longitudinal center line 1. In either event the shoulder region of the round nose configuration from the point of full gauge to the nose is a portion of a circle. The pivot'point for the radius of curvature of the circle would be at the intersection point, e.g. point 12 in FIG. I, of the full gauge radius, 13in FIG. 1 and line 10, FIG. I; 1

The shape of the bit of this invention provides more I shoulder area than the round nose bit so that the bit of this invention can carry more'diamonds, especially in the high wear shoulder area, than can the round nose bit. The shoulder area of a double-cone bit can be increased by increasing the magnitude of angle-E, FIG. 1, but when this is done the nose portion and the areas immediately adjacent the nose portion of the bit become so sharp as to materially weaken that portion of the bit. In the bit of this invention the radii of curvature immediately adjacent the nose, e.g., radius 31 of FIG. 2, is greater than comparable radii in the double-cone bit, e.g., radius 8 of FIG. 1, so that the nose portion and the areas immediately adjacent the nose portion are not so sharp as to materially weaken the bit of this invention.

FIG. 2 shows the longitudinal cross-sectional configuration of this invention. In the configuration of this invention shoulder region is composed of a modified parabolic shape comprised of two curved sections. The first curved section 21 is defined by moving full gauge radius 22 from the point of full gauge 23 through angle- A to the point of transition 24. The pivotal point 26 for full gauge radius 22 is the point of intersection between longitudinal center line and the full gauge radius line 27 when extending from the point of full gauge 23 and intersecting longitudinal center line 25 at a right angle. It should be noted that the longitudinal center line 25 extends through the center of throat region 28 and intersects the full gauge radius 27 at a right angle. Angle- A varies from about 50 to about 60.

The second curved portion 30 of shoulder 20 is defined by the movement of radius of curvature 31 through angle B from the point of transition 24 to nose 32, more specifically line 33 which extends from the outer side of nose 32, i.e., the side closest to shoulder 20, parallel to longitudinal center line 25, intersecting line 34 (the line between point of transition 24 and pivot point 26) at pivotal point 35. Point 35 is the pivotal point of radius of curvature 31. Radius 31 can be of varying lengths but is less than one-half the length of radius of curvature 22 while angle-B is 90 minus angle-A.

As with FIG. 1, nose region 32 can be of finite width as shown in FIG. 2 or can be merely a point 36 which defines a line that circumscribes throat region 28 and has substantially no width.

The inner side of nose region 32 which is closest to throat region 28 is represented by dotted line 37. Line 37 extends parallel to longitudinal center line 25 and intersects line 34 at point 38 which is the pivotal point for curvature radius 39. Pivotal point 38 can lie anywhere along line 37 down to and including point 38. Radius 39 is of a length less than one-half the length of full gauge radius 22 and defines curved portion 40 of throat region 28 when moved from line 37 through angle-C to point 41. From point 41 to longitudinal center line 25 there is a conical section 42 similar to section 7 of FIG. 1. This conical section is uncurved asshown in the cross-section of FIG. 2 but extends around the central portion of throat region 28. Conical section 42 is at an angle-D with respect to full gauge radius 27. Angle-C generally is from about 30 to about 60 and angle-D equals angle-C.

As with FIG. 1, if desired, conical section 42 in throat region 28 can be eliminated and curved surface 40 extended until it intersects longitudinal center line 25 so that the throat region is composed of a continuous curve rather than a combination of partial curve 40 and a conical section 42. If thelength of radius of curvature 39 is insufficient to" intersect longitudinal center line 25 than a portion of the throat region should be made up of a conical section 42 or a different curved section in order to reach longitudinal center line 25.

Pivotal point 26 at which longitudinal center line 25 intersects full gauge radius 27 at when extending from point of full gauge 23 is defined, in this invention, as the center of the bit. g

Full gauge radius 22, in the slim hole context, can vary from about one-half to about 3 inches. Angle-B can vary from about 30 to about 60 using a radius of curvature 31 of less than one-half the full gauge radius 22.

The specially modified configuration -of FIG; 2 is not a true parabolic configuration because, for a true parabolic configuration, among other things, the radius of curvature defining curved section 21 of shoulder region'20 would not be equal in length to full gauge radius 27, but rather would be of a length substantially less than the length of full gauge radius 27, and the pivot point of the radius of curvature for a true parabolic configuration would not be at center point 26 but rather would be at a point on full gauge radius line 27 intermediate center point 26 and full gauge point 23. Thus, the configuration of FIG. 2 varies substantially from a double-cone configuration, a round nose configuration, and a true parabolic configuration.

The width of nose region 32 can vary from substantially no width up to a finite width of about one sixteenth the length of full gauge radius 27.

In a conventional diamond-type bit there is a shank portion which has thread means on one end for attaching the bit to a drill pipe section. The shank portion is fixed to a crown portion and the crown portion supports the blades or pads which carry the cutting elements. The configuration shown in FIG. 2 applies to both the crown and the blades and/or pads carried by the crown.

One embodiment which can employ the configuration of FIG. 2 is shown in FIG. 3 wherein crown 40 supports three blades 41, 42, and 43. Each of the blades has a water course 41', 42, and 43', which communicates with the open interior 44 of crown 40 so that drilling fluid passing down through the drill pipe, passes through the shank and crown of the bit, through opening 44 and into each of the channels 41 through 43' to provide lubrication, cooling, and the like for the bit during drilling. Each blade carries a plurality of cutting elements 45. Each cutting element 45 can be composed of a single particle of hard material or an agglomeration of hard particles into a single piece. Naturally occurring or synthetic single particles or agglomerations can be used. The hard single particle or the hard particles agglomerated into a single piece, can be composed of any hard material, e.g., natural or synthetic diamonds including natural or synthetic agglomerations of diamond particles, tungsten carbide, cubic boron nitride, metal coated (nickel, chromium, molybdenum, iron and the like) tungsten carbide, etc.

If the bit shown in FIG. 3 were to be converted from a blade bit to a diamond-type bit with conventional pads or lands, a major portion of the space between adjacent blades of FIG. 3 would be taken up by larger area pads the surfaces of which are covered with cutting elements as the blades of FIG. 3 are shown to be covered with cutting elements. In either instance, the crown, blades and/or pads or lands would conform in longitudinal cross-sectional configuration to that shown in FIG. 2, more specifically two lobes 50 and 51, bisected by longitudinal center line 25, each lobe conforming to the configuration as defined for lobe 51 hereinabove.

In the method of this invention the bit according to this invention is attached to a drill pipe string in a conventional manner and a wellbore drilled in a conventional manner except that the wellbore, in the case of slim hole drilling, would have a small diameter, e.g., no larger than about 6 inches, this diameter being determined by the full gaugediameter of the bit, and the drill bit would be rotated during at least part of the drilling at rates of at least about 500, preferably from about 600 to about 2,000, rpm.

EXAMPLE A bit was formed substantially as shown in FIG. 3 and meeting the longitudinal cross-sectional configuration of FIG. 2 wherein full gauge radius 27 is 1 31/32 thirty-seconds seconds inches in length, angle-A is 50, the radius of curvature 31 is three-fourths inches, angle-B is 40, nose region 32 width is substantially 0, radius of curvature 39 is three-fourths inch, angle-C is 30, and angle-D is 30. The individual cutting elements 45 in the blades were formed of diamond particles naturally cemented together (framesite) to form each individual cutting element piece. The full gauge diameter of the bit would drill a substantially 4 inch diameter wellbore.

The bit was employed in drilling a wellbore to a depth of 4,215 feet, rotating the drill bit at an average of l ,000 rpm, utilizing two of the drill bits to reach total depth. During the drilling of the wellbore the average M drilling life for each bit was 31 hours and the average drilling rate was 1.1 feet per minute.

an angle-A of from about 50 to about 60 to a point of transition, the curvature through angle-A using the full gauge radius of the bit as the radius of curvature through said angle-A, and the region between said point of transition and the nose of said bit curving through an angle-B of minus angle-A using a radius of curvature less than onehalf the full gauge radius of the bit, the pivot point of said radius of curvature through said angle-B being along the line which extends between said point of transition and the center of said bit.

2. A bit according to claim 1 wherein at least the part of the throat region adjacent the nose region is curved through an angle-C using a radius of curvature less than one-half the full gauge radius of thebit, the pivot point of said radius of curvature through said angle-C being along the line between said point of transition and the center of said bit.

3. A bit according to claim 2 wherein the central part of the throat region is substantially a conical ction.

4. A bit according to claim 1 wherein the ull gauge radius varies from about one-half to about 3 inches, part of the throat region adjacent the nose region is curved through an angle-C of from about 30 to about 60 using a radius of curvature less than one-half the full gauge radius of the bit, the pivot point of said radius of curvature through said angle-C being along the line between said point of transition and the center of said bit, the remaining central part of the throat region being substantially a conical section at an angle-D, angle-D equals angle-C.

5. A bit according to claim 4 wherein said nose region has a finite width.

6. A bit according to claim 1 wherein the full gauge radius varies from about one-half to about 3 inches, and the throat region is curved through an angle-C of about 90 usinga radius of curvature less than one-half the full gauge radius of the bit, the pivot point of said radius of curvature through said angle-C being along the line between said point of transition and the center 

1. In a bit having throat, nose, and shoulder regions, the improvement comprising the bit having a double-lobed essentially parabolic cross-sectional configuration as shown in FIG. 2, in each lobe the shoulder region starting at the point of full gauge curving through an angle-A of from about 50* to about 60* to a point of transition, the curvature through angle-A using the full gauge radius of the bit as the radius of curvature through said angle-A, and the region between said point of transition and the nose of said bit curving through an angle-B of 90* minus angle-A using a radius of curvature less than one-half the full gauge radius of the bit, the pivot point of said radius of curvature through said angle-B being along the line which extends between said point of transition and the center of said bit.
 2. A bit according to claim 1 wherein at least the part of the throat region adjacent the nose region is curved through an angle-C using a radius of curvature less than one-half the full gauge radius of the bit, the pivot point of said radius of curvature through said angle-C being along the line between said point of transition and the center of said bit.
 3. A bit according to claim 2 wherein the central part of the throat region is substantially a conical section.
 4. A bit according to claim 1 wherein the full gauge radius varies from about one-half to about 3 inches, part of the throat region adjacent the nose region is curved through an angle-C of from about 30* to about 60* using a radius of curvature less than one-half the full gauge radius of the bit, the pivot point of said radius of curvature through said angle-C being along the line between said point of transition and the center of said bit, the remaining central part of the throat region being substantially a conical section at an angle-D, angle-D equals angle-C.
 5. A bit according to claim 4 wherein said nose region has a finite width.
 6. A bit according to claim 1 wherein the full gauge radius varies from about one-half to about 3 inches, and the throat region is curved through an angle-C of about 90* using a radius of curvature less than one-half the full gauge radius of the bit, the pivot point of said radius of curvature through said angle-C being along the line between said point of transition and the center of said bit.
 7. A bit according to claim 6 wherein said nose region has a finite width. 